Method of fabricating a bobbin and core assembly

ABSTRACT

A disc of a nonmagnetic malleable material is forced within a center tubular portion of a nonmagnetic bobbin with an elongated cylindrical core of a magnetic material. The diameter of the disc is greater than the inside diameter of the tubular portion, the core is adapted to be closely received longitudinally within the tubular portion, and as the disc is forced within the restricted opening of the tubular portion by the core it is folded around the end of the core and secured thereto. Continued movement of the core, with the disc secured to the end thereof, through the tubular portion and slightly past the end thereof forms the bobbin and core assembly.

United States Patent 1191 Ciszewski 1 Jan. 22, 1974 [75] Inventor: Raymond S. Ciszewslri, Lagrange,

Ill.

[73] Assignee: Western Electric Company,

Incorporated, New York, N.Y.

221 Filed: Dec.18,l972

21 Appl. No.: 316,196

[52] US. Cl 29/602, 29/445, 29/517, 29/525, 29/606, 335/271, 335/277, 336/198 [51] Int. Cl. H0lf 7/06 [58] Field of Search 29/596, 602, 606; 336/198; 310/17; 335/271, 277; 29/445, 525, 517

2,725,616 12/1955 Epstein ..29/606 Primary Examiner-Charles W. Lanham Assistant Examiner-Carl E. Hall Attorney, Agent, or Firm-R. A. Lloyd [5 7 ABSTRACT A disc of a nonmagnetic malleable material is forced within a center tubular portion of a nonmagnetic bobbin with an elongated cylindrical core of a magnetic material. The diameter of the disc is greater than the inside diameter of the tubular portion, the core is adapted to be closely received longitudinally within the tubular portion, and as the disc is forced within the restricted opening of the tubular portion by the core it is folded around the end of the core and secured thereto. Continued movement of the core, with the disc secured to the end thereof, through the tubular portion and slightly past the end thereof forms the bobbin and core assembly.

4 Claims, 3 Drawing Figures METHOD OF FABRICATING A BOBBIN AND CORE ASSEMBLY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of fabricating a bobbin and core assembly, and in particular to a method of fabricating a bobbin and core assembly, for use in an electromagnetic device, wherein a core of magnetic material, extended through a bobbin of nonmagnetic material, has a residual element secured to the end thereof.

2. Description of the Prior Art With electromagnetic operating coils, an air gap is normally required between a core of the coil and an armature actuated thereby to negate the effects of residual magnetism which could reduce the operating time of the armature. In fabricating such electromagnetic coils, it is customary to achieve the effect of an air gap by fastening a residual element of a nonmagnetic material, such as brass, to the end of the core to ensure a minimum spacing between the end of the core and the armature actuated thereby, and therefore to obtain a quick armature release upon deenergization of the coil and destruction of the magnetic field within the core.

A present method of fabricating bobbin and core assemblies for electromagnetic operating coils having such residual elements, wherein unitary, molded bobbins are employed, is to stake, or crimp, a residual element cap, or plate, to the end of a core of magnetic material, and to then extend the core through the center of the bobbin. This present method is expensive and time consuming in that two operations are involved; that is, the residual element must first be secured to the end of the core, and then the core must be extended through the center of the bobbin.

SUMMARY OF THE INVENTION In accordance with the present invention, a cap of a malleable material is secured to an end of a cylinder extended through and closely received within a tubular member, the cylinder having an annular recess near a forward end thereof, by pushing a disc of the malleable material, having a diameter greater than the inner diameter of the tubular member, into an end of the tubular member with the forward end of the cylinder. This forms the disc into a cap around the end of the cylinder and into the annular recess as the disc enters the smaller diameter opening of the tubular member. The cylinder is then extended through the tubular member and the formed disc is secured, as the end of the cylinder exits from the tubular member, to hold the cylinder from axial movement.

Preferably, the cap of the malleable material is a residual element of nonmagnetic material which is secured to an end of a cylindrical core of magnetic material within a unitary bobbin of nonmagnetic material. In this case, the bobbin has a hollow tubular center portion, for closely receiving the core, with first and second flanges at first and second ends of the center portion, respectively. The first flange has on its outside surface an annular ridge, coaxial with the center of the tubular portion, having an inner diameter greater than the diameter of the center of the tubular portion. The tubular portion has at its second end a narrow, circumferential lip extending radially inward of the center portion, the lip having an inner diameter slightly less than the inner diameter of the center portion. The cylindrical core has a truncated conical formation at a first end thereof, with the base of the conical portion defining an end of the core. This forms a circumferential groove in the core, at the first end thereof, between the base and the truncation of the conical portion. Also, the base of the conical portion has a diameter slightly less than the diameter of the cylindrical portion of the core.

To assemble the residual element, the core and the bobbin, a flat, malleable disc of nonmagnetic material is positioned within the annular ridge on the first flange, the disc having a diameter approximately equal to the inside diameter of the annular ridge and therefore greater than the inside diameter of the center portion of the bobbin. The cylindrical core is then positioned coaxial with the center tubular portion of the bobbin, with the first end of the core adjacent the malleable disc, and is moved against the disc and into the center tubular portion of the bobbin. This forces the disc into the center portion and around the conical end of the core, with the center of the disc conforming to the base of the conical end and with the edges of the disc folding around the periphery of the base and into the circumferential groove as the disc is forced within the smaller diameter opening of the center portion. This folding of the disc forms a residual element on the first end of the core.

Continued movement of the core then carries the first end of the core, with the disc secured thereto, through the center portion of the bobbin, forcefully past the circumferential lip at the second end of the center portion, and partially beyond the second end of the center portion. With the core in this position, the circumferential ridge is received within the groove, and against the portion of the disc folded therewithin, to secure the core within the center portion of the bobbin with the end of the core having the residual element thereon extending slightly beyond the end of the bobbin.

Other objects, advantages and features of the invention will be apparent upon consideration of the following detailed description when taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the arrangement of the components of a bobbin and core assembly prior to being operated upon in accordance with the method of the invention;

FIG. 2 is a sectional view of the assembled bobbin, core and residual element, and

FIG. 3 is a view of the end of the core having the residual element thereon.

DETAILED DESCRIPTION The bobbin and core assembly as shown in the drawings, to be assembled in accordance with the method of the invention, includes an integrally molded coil bobbin 12 of any plastic insulating material having some degree of resilience to permit deformation thereof, a core piece 16 of magnetic iron or any other suitable magnetic material, and a residual element 20 which may be of brass or any other malleable nonmagnetic material.

The molded bobbin 12 has a hollow tubular portion 24 with first and second flanges 28 and 32 at the opposite ends thereof. The flange 28 includes two conductive terminals 36 and 40 embedded partially therewithin and adapted to receive opposite ends of a coil of wire (not shown) which may be wound on the tubular portion 24 between the flanges 28 and 32. The flange 28 also has formed on the outside surface thereof an annular ridge 44, which is coaxial with the tubular portion 24, and which has a greater inner diameter than the inner diameter of the tubular portion 24 as defined by an inner surface 48 thereof. As shown in FIG. 2, a narrow circumferential lip 52 is formed on the inner surface 48 of the tubular portion 24, at the end thereof having the flange 32, to slightly restrict, at that end, the inner diameter of the tubular member 24. Alternatively, the circumferential lip 52 may be considered as being defined by an inner diameter of the flange 32, such that the flange 32 presents a restricted opening to the inner portion of the tubular member 24, as compared with the unrestricted opening presented by the inner diameter of the flange 28 to the inner portion of the tubular member 24.

Y The magnetic material core 16 is adapted to be closely received within the tubular portion 24 of the bobbin 12, and is formed of an elongated cylindrical body portion 56 having a truncated conical formation 60 at one end thereof. The conical formation 60 has a base 64 which defines one end of the core 16, and is integrally joined or formed with the cylindrical body portion 56 at the truncation thereof. A circumferential groove 68 is formed in the core 16 between the base 64 of the conical portion 60 and the truncation thereof which joins with the cylindrical body portion 56 of the core 16. The diameter of the body portion 56 is essentially equal to the inner diameter of thetubular portion 24 so that the core 16 may be closely received within the bobbin 12, while the diameter of the base 64 is slightly less than the inner diameter of the tubular portion 24, and therefore less than the diameter of the body portion 56, for reasons that will later be apparent.

The core 16 also has a knurl 72 peripherally around the surface thereof at the opposite end of the cylindrical body portion 56 from the truncated conical formation 60. The knurl 72 engages the inner surface 48 of the tubular portion 24 when the core 16 is inserted therein to retard rotary movement of the core 16 within the bobbin 12.

To assemble the bobbin and core with the residual element secured to an end of the core, a thin disc 76 of malleable material, such as brass, is positioned within the annular ridge 44 on the flange 28, the sole purpose of which is to receive and position thedisc 76, and on a surface 80 of the flange 28 defined within the annular ridge 44. The diameter of the disc 76 is approximately equal to the inner diameter of the annular ridge 44, and is therefore greater than the inner diameter of the tubular portion 24. Then, with the bobbin 12 resting with the flange 32 on a die 84, the core 16 is positioned coaxial with the tubular portion 24, with the base 64 of the conical formation 60 resting against the disc 76, and is driven against the disc 76 and into the center of the tubular portion 24 with a punch 88.

As the disc 76, having a larger diameter than the inside diameter of the tubular portion 24, is forced into the center of the tubular portion 24 by the core 16, the

peripheral edges of the disc 76 are folded around the periphery of the base 64 of the conical portion 60 and into the circumferential groove 68, while the center portion of the disc 76 conforms to the base 64 of the conical portion 60. While the disc 76 in FIG. 2 is shown with its peripheral edge folded smoothly around the conical portion 60, it is to be appreciated that in actual practice folding, or pleating, of the peripheral edge occurs within the groove 68 to accommodate excess material, as shown in FIG. 3. This folding of excess material of the disc 76 within the groove 68 of the conical portion 60 as the core 16 enters the center of the bobbin 12 secures the now cap shaped disc 76 to the end of the core 16 and forms the residual element 20 thereon. It should not be apparent that the base 64 of the conical portion 60 has a diameter slightly smaller than the diameter of the cylindrical body portion 56 of the core 16 in order to accommodate formation of the disc 76 therearound when the disc and core are forced within the bobbin l2.

Continued movement of the core 16 through the center of the bobbin 12 under the influence of the punch 88 forcefully carries the base 64 of conical portion 60, having the residual element 20 therearound, past the circumferential lip 52, slightly exterior of the opposite end of the bobbin 12, and within an aperture 92 formed in the die 84. When the base 64 of the conical portion 60, having the residual element 20 formed thereon, engages the circumferential lip 52 of the bobbin 12, the lip 52 is deformed to permit movement of the residual element and base therepast. As the base 64 of the conical formation 60 moves past the lip 52, the lip 52 enters within the circumferential groove 68 with an inner surface 96 of the lip 52 forcefully engaging and essentially conforming in shape with the folded peripheral edges of the disc 76. This additionally secures the residual element 20 to the core 16 and further functions to arrest axial movement of the core 16 within the bobbin 12. The length of the core 16 is slightly greater than the length of the bobbin l2, and in the complete assembly extends at each of its ends slightly beyond the bobbin 12. With the core 16 assembled within the bobbin 12, the knurl 72 thereof engages the inner surface 48 of the tubular portion 24 to prevent rotary movement of the core 16 within the bobbin 12.

While one embodiment of the invention has been described in detail, it is understood that various other modifications and embodiments may be devised by one skilled in the art without departing from the spirit and scope of the invention. For example, while the annular ridge 44 on the flange 28 has been described for the purpose of positioning the disc 76 relative to the center tubular portion 24 prior to insertion of the disc therein, the disc may just as readily be positioned within a circular cavity formed in the flange 28 coaxial with the tubular portion 24.

What is claimed is:

1. In a method of securing a malleable material to the end of a cylinder extended through and closely received within a tubular member, the cylinder having an annular recess near a forward end thereof;

pushing a disc of the malleable material, having a diameter greater than the inner diameter of the tubular member, into an end of the tubular member with the forward end of the cylinder to form the disc around the end of the cylinder and into the annular recess as the disc enters the smaller diameter opening of the tubular member, the pushing being continued to extend the cylinder into and through the tubular member, and

securing the formed disc to the tubular member, as

the end of the cylinder exits from the tubular member, to hold the cylinder from axial movement in the tubular member. 2. In a method of fabricating an electromagnetic device having a nonmagnetic coil bobbin with a hollow tubular center portion, a cylindrical core of magnetic material extended through and closely received within the tubular center portion of the bobbin, and a residual element of nonmagnetic material secured to an end of the core:

positioning a flat circular disc of a malleable, residual element material, having a diameter greater than the inner diameter of the hollow center portion of the bobbin, over one end of the center portion with the axis of the disc in alignment with the axis of the center portion; forcing the disc within and through the tubular center portion with the cylindrical core to fold the edges of the disc around, and to secure the disc to, the engaging end of the cylindrical core as the disc is forced within the smaller diameter of the center portion, and to extend the tip of the cylindrical core having the disc secured thereto through the tubular center portion of the bobbin, and

fastening the disc, secured to the tip of the core, to

the tubular center portion as the disc exits the center portion of the bobbin, to hold the core against axial movement in the bobbin.

3. In a method as set forth in claim 2, wherein the core is formed in an elongated cylinder having a truncated conical portion at one end thereof, with the base of the conical portion defining one end of the core to form a circumferential groove in the core, at the end of the core, between the base and the truncation of the conical portion, and wherein the tubular center portion has a radial projection on the interior surface at one end thereof for entering the circumferential groove when the core is inserted within the center portion, wherein:

in the positioning step, the disc is positioned over the end of the center portion opposite the radial projection, and

the forcing step comprises pushing the disc within and through the tubular center portion with the base of the conical portion of the core, to fold the edges of the disc around the base and within the circumferential groove as the disc enters the center portion, and to push the base of the conical portion of the core past the radial projection to engage at least a portion of the edge of the disc within the groove with the radial projection. 4. In a method of assembling a nonmagnetic residual element to the end of a cylindrical core of magnetic material within a unitary bobbin of nonmagnetic material, the bobbin having a hollow tubular center portion, for closely receiving the core, with first and second flanges at first and second ends of the center portion, respectively, the first flange having on its outside surface an annular ridge coaxial with the center of the tubular portion and having an inner diameter greater than the diameter of the center of the tubular portion, and the tubular portion having at its second end a narrow circumferential lip extending radially inward of the center portion and having an inner diameter slightly less than the inner diameter of the center portion, the cylindrical core having a truncated conical formation at a first end thereof, with the base of the conical formation defining an end of the core and forming a circumferential groove in the core between the base and the truncation of the conical formation, the base of the conical formation having a diameter slightly less than the diameter of the cylindrical portion of the core:

positioning a flat, malleable disc of nonmagnetic material within the annular ridge on the first flange, the disc having a diameter approximately equal to the inside diameter of the annular ridge and therefore greater than the inside diameter of the center portion of the bobbin; positioning the core coaxial with the center tubular portion of the bobbin, with the base of the conical formation adjacent the malleable disc, and

moving the core against the disc and into the center tubular portion of the bobbin, to force the disc into the center portion and around the conical end of the core with the center of the disc conforming to the base of the conical end and with the peripheral edges of the disc folding around the periphery of the base and into the circumferential groove in the core as the disc is forced within the restricted opening of the center portion, the disc forming a residual element on the first end of the core, and to pass the first end of the core, with the disc secured thereto, through the center portion of the bobbin, forcefully past the circumferential ridge at the second end of the center portion, and partially beyond the second end of the center portion with the circumferential ridge being received within the groove, and against the portion of the disc folded therewithin, to secure the core within the center portion of the bobbin with the end of the core having the residual element thereon extending slightly beyond the end of the bobbin. 

1. In a method of securing a malleable material to the end of a cylinder extended through and closely received within a tubular member, the cylinder having an annular recess near a forward end thereof; pushing a disc of the malleable material, having a diameter greater than the inner diameter of the tubular member, into an end of the tubular member with the forward end of the cylinder to form the disc around the end of the cylinder and into the annular recess as the disc enters the smaller diameter opening of the tubular member, the pushing being continued to extend the cylinder into and through the tubular member, and securing the formed disc to the tubular member, as the end of the cylinder exits from the tubular member, to hold the cylinder from axial movement in the tubular member.
 2. In a method of fabricating an electromagnetic device having a nonmagnetic coil bobbin with a hollow tubular center portion, a cylindrical core of magnetic material extended through and closely received within the tubular center portion of the bobbin, and a residual element of nonmagnetic material secured to an end of the core: positioning a flat circular disc of a malleable, residual element material, having a diameter greater than the inner diameter of the hollow center portion of the bobbin, over one end of the center portion with the axis of the disc in alignment with the axis of the center portion; forcing the disc within and through the tubular center portion with the cylindrical core to fold the edges of the disc around, and to secure the disc to, the engaging end of the cylindrical core as the disc is forced within the smaller diameter of the center portion, and to extend the tip of the cylindrical core having the disc secured thereto through the tubular center portion of the bobbin, and fastening the disc, secured to the tip of the core, to the tubulAr center portion as the disc exits the center portion of the bobbin, to hold the core against axial movement in the bobbin.
 3. In a method as set forth in claim 2, wherein the core is formed in an elongated cylinder having a truncated conical portion at one end thereof, with the base of the conical portion defining one end of the core to form a circumferential groove in the core, at the end of the core, between the base and the truncation of the conical portion, and wherein the tubular center portion has a radial projection on the interior surface at one end thereof for entering the circumferential groove when the core is inserted within the center portion, wherein: in the positioning step, the disc is positioned over the end of the center portion opposite the radial projection, and the forcing step comprises pushing the disc within and through the tubular center portion with the base of the conical portion of the core, to fold the edges of the disc around the base and within the circumferential groove as the disc enters the center portion, and to push the base of the conical portion of the core past the radial projection to engage at least a portion of the edge of the disc within the groove with the radial projection.
 4. In a method of assembling a nonmagnetic residual element to the end of a cylindrical core of magnetic material within a unitary bobbin of nonmagnetic material, the bobbin having a hollow tubular center portion, for closely receiving the core, with first and second flanges at first and second ends of the center portion, respectively, the first flange having on its outside surface an annular ridge coaxial with the center of the tubular portion and having an inner diameter greater than the diameter of the center of the tubular portion, and the tubular portion having at its second end a narrow circumferential lip extending radially inward of the center portion and having an inner diameter slightly less than the inner diameter of the center portion, the cylindrical core having a truncated conical formation at a first end thereof, with the base of the conical formation defining an end of the core and forming a circumferential groove in the core between the base and the truncation of the conical formation, the base of the conical formation having a diameter slightly less than the diameter of the cylindrical portion of the core: positioning a flat, malleable disc of nonmagnetic material within the annular ridge on the first flange, the disc having a diameter approximately equal to the inside diameter of the annular ridge and therefore greater than the inside diameter of the center portion of the bobbin; positioning the core coaxial with the center tubular portion of the bobbin, with the base of the conical formation adjacent the malleable disc, and moving the core against the disc and into the center tubular portion of the bobbin, to force the disc into the center portion and around the conical end of the core with the center of the disc conforming to the base of the conical end and with the peripheral edges of the disc folding around the periphery of the base and into the circumferential groove in the core as the disc is forced within the restricted opening of the center portion, the disc forming a residual element on the first end of the core, and to pass the first end of the core, with the disc secured thereto, through the center portion of the bobbin, forcefully past the circumferential ridge at the second end of the center portion, and partially beyond the second end of the center portion with the circumferential ridge being received within the groove, and against the portion of the disc folded therewithin, to secure the core within the center portion of the bobbin with the end of the core having the residual element thereon extending slightly beyond the end of the bobbin. 